Airborne Infrasound Makes a Splash

Abstract

Acoustic waves can travel vast distances in planetary atmospheres. These waves convey information both on the source that generated them as well as the properties of the medium they travel through. On Earth, these acoustic waves typically fall in the "infrasound" range (<20 Hz, the lower limit of human hearing), since higher frequency waves attenuate more quickly. Infrasound waves can circle the globe multiple times given a powerful enough source (Le Pichon et al., 2013;Symons, 1888).A variety of natural and anthropogenic phenomena gives rise to infrasound. Discrete natural events such as bolide airbursts (Ens et al., 2012;Silber et al., 2009), large earthquakes (Le Pichon et al., 2005;Shani-Kadmiel et al., 2021), and volcanic eruptions (Fee & Matoza, 2013) create signals that can travel over regional to global scales. Other activity such as colliding ocean waves (the "ocean microbarom") (Waxler & Gilbert, 2006), wind blowing over mountains (Bedard, 1978;Walterscheid & Hickey, 2005), and severe storms (Goerke & Woodward, 1966) can create long duration signals that comprise much of the Earth's infrasonic background at low frequencies. Regional to local infrasound (and occasionally audible emissions) have been reported from small earthquakes (

The Utility of Infrasound in Global Monitoring of Extraterrestrial Impacts: A Case Study of the 2008 July 23 Tajikistan Bolide

“…Events like this one also attest to the importance of having accurate atmospheric specifications and the need to continuously refine propagation models. Moreover, future observations of bolides from an elevated vantage point using stratospheric balloons hold the potential to significantly enhance the detection efficiency compared to ground-based sensing methods (e.g., Young et al 2018;Bowman 2021;Albert et al 2023). Because balloons float in the region of the atmosphere where the AtmoSOFAR channel forms, these sensing platforms could potentially detect signals from high-altitude sources such as bolides or supersonic vehicles at very large distances.…”

“…Observations of large bolide impacts on a global scale are of the utmost importance for a number of reasons, including planetary defense, impact risk hazard assessment, event characterization, and improving global monitoring efforts (e.g., Chapman 2008;Christie & Campus 2010;Mainzer 2017;Silber et al 2018;Trigo-Rodríguez 2022). Current monitoring technologies include ground instruments (e.g., dedicated camera systems, infrasound, and radar; e.g., Janches et al 2006;Koschny et al 2017;Silber & Brown 2019;Drolshagen et al 2021), floating platforms (e.g., scientific payloads suspended on high-altitude balloons; Young et al 2018;Bowman 2021), and space-based assets (e.g., U.S. government or USG sensors and the Geostationary Lightning Mapper or GLM instrument; Nemtchinov et al 1997;Jenniskens et al 2018;Ott et al 2021;Morris et al 2022). These technologies can work in unison or independently, depending on circumstances, geographical coverage, the energetics of the event, and data availability.…”

“…Further to this, some of these technologies are more "mature" (e.g., video camera detections) than others (e.g., McCrosky & Ceplecha 1968;Ceplecha 1977;Hawkes et al 1984). Balloon infrasound, for example, while a promising method for Earth-based surveillance as well as future extraterrestrial exploration (Bowman 2021;Krishnamoorthy & Bowman 2023), is still considered an emerging technology. On the other hand, ground-based infrasound surveillance has been around off and on since the early 1960s (see Section 2; Revelle 1997;Christie & Campus 2010).…”

Isolating the Source Region of Infrasound Travel Time Variability Using Acoustic Sensors on High-Altitude Balloons

“…Emplacement of microbarometers on high-altitude floating platforms offers advantages such as monitoring regions of Earth (e.g., oceans) that are inaccessible to other sensing modalities and directly probing acoustic propagation channels in Earth's atmosphere [10,15]. Another key application of such systems is the exploration of extraterrestrial planets with harsh atmospheres, e.g., Venus [16,17] or gas giants [18]. Considering that the horizontal motion of a balloon is driven by prevailing stratospheric winds, the level of wind-induced background noise is also presumably lower than that in a ground-based sensing environment [19], although a recent study noted the presence of numerous as yet unidentified sources of relatively high noise in one data set [20].…”

Topographically Scattered Infrasound Waves Observed on Microbarometer Arrays in the Lower Stratosphere

“…Infrasound can be used to monitor a variety of sources, including earthquakes (e.g., Arrowsmith et al., 2012), volcanic eruptions (e.g., Johnson & Ripepe, 2011), ocean processes (e.g., Fricke et al., 2014), urban activity (e.g., Bird et al., 2021), and nuclear or chemical explosions (e.g., Che et al., 2009; Pasyanos & Kim, 2019). The bulk of infrasound research focuses solely on data from ground‐based sensors, but a growing area of study considers airborne stations (Bowman, 2021). Recordings from infrasound microphones attached to balloons, aerostats, or other similar crafts have been used to interrogate numerous sources, including microbaroms (Bowman & Lees, 2015), volcanism (Jolly et al., 2017), chemical explosions (Bowman et al., 2014), sonic booms (Veggeberg, 2012), and ground shaking (Krishnamoorthy et al., 2018).…”